Life activity is connaturally accompanied with various cyclic changes ranging from the behavior at the individual level to the biochemical phenomena at the cellular level. These rhythmic life activities occurring at certain cycles are called biorhythm and a periodic length of these phenomena which are repeated in cycles is often close to a periodic fluctuation of the environment such as a year, a month or a day. Sleep-wake rhythm and hormonal-secretion rhythm for such as melatonin and the adrenal cortex hormone are among those representing circadian rhythms repeated by an approximately 24-hour cycle, a daily unit. The circadian rhythms as mentioned have been observed in almost all the biological species and tissues and are regulated by the biological clock (Annu. Rev. Physiol. 55, 16–54, 1993). The suprachiasmatic nucleus (SCN) in the vertebrate central nervous system, pineal gland, specific neuronal tissues such as retina, etc. are known as tissues conforming circadian rhythm (Science 203, 1245–1247, 1979, Science 203, 656–658, 1979, Proc. Natl. Acad. Sci. USA 76, 999–1003, 1979, Brain Res. 245, 198–200, 1982, Neuron 10, 573–577, 1993, Science 272, 419–421, 1996).
As in the case of the mammalian suprachiasmatic nucleus (SCN), non-mammalian vertebrate pineal glands produce melatonin in response to circadian rhythm and light stimuli and play a central role in the physiological circadian regulation (Science 203, 1245–1247, 1979, Science 203,656–658, 1979, Proc. Natl. Acad. Sci. USA 76, 999–1003, 1979, Proc. Natl. Acad. Sci. USA 77, 2319–2322, 1980, Proc. Natl. Acad. Sci. USA 80, 6119–6121, 1983, J. Neurosci. 9, 1943–1950, 1989). The oscillation mechanism of the above-mentioned circadian rhythm is said to be characterized by the system wherein oscillation occurs at the gene level, is then amplified at the cellular level and finally reaches the individual level (Cell 96, 271–290, 1999). Oscillation at the gene level is brought by a group of genes called clock genes. Recent studies on the rodent clock genes have revealed that the circadian oscillator genes in mammals are positive and negative elements which form the transcription/translation-based negative feedback loop (Cell 96, 271–290, 1999, Annu. Rev. Neurosci. 23, 713–742, 2000). In mice, the negative elements include three period gene homologs; Perl (Cell 90, 1003–1011,1997, Nature 389,512–516,1997), Per2 (Cell 91, 1055–1064, 1997, Neuron 19, 1261–1269, 1997, Genes Cells 3, 167–176, 1998) and Per3 (EMBO J. 17, 4753–4759, 1998, Neuron, 20, 1103–1110, 1998) and two cryptochrome homologs; Cryl and Cry2 (Cell 98, 193–205, 1999, Nature 398, 627–630, 1999).
As for positive elements, BMAL1, CLOCK and the like which are basic helix-loop-helix (bHLH)-PAS (Per-Arnt-Sim) transcription elements are known. A CLOCK-BMAL1 complex is known to activate transcription through an E-box sequence (E-box: CACGTG) which is found not only in the negative element Perl (Science 280, 1564–1569, 1998) but also in clock-controleed genes such as vasopressin (Cell 96, 57–68, 1999) and in the albumin D-site binding protein gene (Genes Dev.14, 679–689, 2000). When a protein level of a negative element mentioned above is increased, its own transactivation for a promoter induced by a positive element is suppressed, the mRNA and protein levels of the negative element are down-regulated, and the molecular cycle is recommenced concomitant with the transactivation of the negative element gene. Therefore, the protein and mRNA levels of a negative element display a marked circadian oscillation. In addition to fluctuations in these clock genes, Perl and Per2 expressions are induced by light (Cell 91, 1055–1064, 1997, Neuron 19, 1261–1269, 1997, Cell 91, 1043–1053, 1997) and at least photo synchronization of an oscillatorisinducedbyPerl (J. Neurosci. 19,1115–1121,1999). Further, it has been revealed that mRNA levels of a positive element Bmall also exhibit circadian oscillation in antiphase to those of negative elements (Biochem. Biophys. Res. Commun. 250, 83–87, 1998, Biochem. Biophys. Res. Commun. 253, 199–203, 1998). Since its transcriptional rhythm is close to that of the Drosophila dClock (Science 286, 766–768, 1999), Bmall is thought to be involved in feedback loop of the negative elements (Science 286, 2460–2461, 1999, Science 288, 1013–1019, 2000).
On the other hand, the chicken (chick) pineal gland has been known that it retains the circadian oscillator as well as photic-input pathway and melatonin-output pathway in the pineal cell and that these properties can readily be retained under culturedconditions (Science 203, 1245–1247, 1979, Science 203, 656–658, 1979, Proc. Natl. Acad. Sci. USA 77, 2319–2322, 1980, Brain Res.438, 199–215, 1988, Recent Prog. Horm. Res. 45, 279–352, 1989, Nature 372, 94–97, 1994, Proc. Natl. Acad. Sci. USA 94, 304–309, 1997, Brain Res. 774, 242–245, 1997). On the basis of these observations, the chick pineal cell is thought to be a prominent model for the study of the vertebrate circadian clock systems at the cellular level (Recent Prog. Horm. Res. 45, 279–352, 1989).
It is known that the biological clock is an auto-oscillatory system which oscillates autonomically without any exogenous stimulation and which, at the same time, has a property of being reset by the exogenous light-stimulation. It is also known that the vertebrate biological clock (circadian clock) which autonomically oscillates in a period close to a day is driven by the auto-feedback-loop consisting of a negative element and a positive element. Many things, however, still remain unknown with regard to the molecular clock system and the like including photic-input and output pathways. The object of the present invention is to provide novel proteins BMAL2 (Brain-Muscle-Arnt-Like protein 2) crucial in the clock oscillation mechanism including photic-input and output pathways, genes encoding the proteins, a method for screening a promoter or a suppressor of the promoter transactivation using the proteins, and the like.